Consumer Unit Explained | Fusebox Safety Guide

Know the controls

Five labels you may see behind the normal flap.

Main switchTurns off the installation

Provides a way to isolate the consumer installation. Some separate equipment may have its own isolation.

MCBProtects one circuit

A miniature circuit breaker responds to overload and short-circuit current.

RCDDetects leakage

A residual current device may protect a group of circuits and normally has a “T” or “Test” button.

RCBOTwo protections combined

Protects an individual circuit against both overcurrent and residual current.

SPDLimits voltage surges

A surge protective device helps protect the installation and equipment from transient overvoltage.

Real consumer-unit examples

Different layouts can provide very different levels of protection.

These are genuine consumer units encountered during SL4 work. The front labels and test buttons can help identify the general arrangement, but a photograph cannot confirm that the wiring, connections or protective devices operate correctly.

Modern metal consumer unit with individual RCBO protection and surge protection — Modern exampleIndividual RCBO protectionEach labelled circuit has its own combined overcurrent and residual-current device. A fault on one circuit is less likely to switch off unrelated circuits.

Older split-load consumer unit with one RCD protecting a group of circuits — Older exampleSplit-load RCD boardOne RCD protects a group of circuits while other circuits may have only MCB protection. The exact coverage must be checked from the device arrangement and testing.

Dual-RCD consumer unit with circuit breakers arranged in two protected groups — Common existing layoutDual-RCD consumer unitCircuits are divided between two RCDs. A fault can disconnect several circuits in the same group, unlike individual RCBO protection.

Look only through the normal user flap. Never remove a screwed cover. Internal parts may remain dangerously live even when a switch appears to be off.

If something trips

A protective device switching off is information—not an inconvenience to defeat.

01
Look and smell before touching the switchesIf there is smoke, burning, scorching, crackling or unusual heat, keep away and treat it as urgent.
02
Identify what has switched offUse only the normal user controls and labels. Never remove the screwed cover.
03
Disconnect a suspect appliance if safeIf the problem began when an appliance was used, unplug it only when there is no damage, heat or immediate danger.
04
Do not keep resetting itIf it trips again, will not reset or the cause is unclear, leave the affected circuit off and arrange fault-finding.

Never tape, wedge or hold a protective device in the on position. Do not replace a fuse with a higher rating or bypass an RCD.

Safe visual checks

What you can check without opening the unit.

Clear circuit labelsLabels should help identify which control supplies lights, sockets, cooking equipment and other circuits.

RCD test buttonsLook for “T” or “Test”. Follow the label and manufacturer’s instructions when operating them.

No heat damageScorching, melting, discolouration, burning smells or crackling require prompt professional attention.

Clear space around itDo not store paper, clothing, cleaning products or other combustible materials around the meter and consumer unit.

Authoritative guidanceElectrical Safety First: home electrical checks ↗IET protective-device guidance ↗

See labelled examples of an MCB, RCD, RCBO and common consumer-unit layouts →

Old does not answer the question

Condition and protection matter more than colour alone.

A plastic enclosure, rewireable fuses or a unit with limited RCD protection may indicate an older design, but a photograph cannot establish the condition of the connected wiring or confirm that a full replacement is required. An inspection considers the complete installation and any planned work.

If the unit is damaged, has no identifiable RCD protection, regularly trips or has no reliable inspection history, ask for an assessment rather than waiting for a failure.

Common questions

What homeowners usually ask.

Does an old fusebox automatically mean the house needs rewiring?

No. Age or appearance alone does not prove that a full rewire is required. An EICR can assess the wiring, earthing, protective devices and overall condition, then separate safety defects from recommended improvements.

Why does a breaker keep tripping?

Possible causes include a faulty appliance, damaged wiring, moisture, an overloaded circuit or cumulative leakage. A single reset may restore power, but repeated tripping needs investigation rather than repeated resetting.

Can I remove the consumer-unit cover?

No. Only open the normal hinged flap intended for the user. Never remove a screwed front cover or touch internal parts; dangerous live components may remain present even when switches are off.